The present invention is directed to thin solid electrolytic capacitors which are particularly suitable for embedding in a substrate and are surface mountable by conventional means. More particularly, the present invention is directed to a method of forming a thin solid electrolytic capacitor which is particularly suitable for embedding in a substrate and is surface mountable by conventional means.
Capacitors are utilized in virtually every electronic device. Their function in an electronic circuit is well known and further discussion is not warranted herein. The instant disclosure is directed to improvements in the manufacture of sheet based capacitors.
In one method of manufacture, capacitors are formed from metal sheets wherein the general process includes oxidation, or anodization, of a valve metal sheet to form a dielectric oxide, thus defining the anode (the valve metal substrate) and the dielectric of the finished device. A conductive layer is then formed on the dielectric, forming the initial cathode contact to the dielectric. The capacitor is conventionally utilized in an electrical circuit with the metal sheet functioning as the anode and the conductive layer functioning as the cathode even though this can be reversed to some degree.
Small surface mount capacitors have been successfully formed from metal foil and particularly aluminum foil. The foil, in either strip or sheet form, is typically etched to increase the surface area and then anodized to form a thin dielectric oxide on each face. A conductive layer, such as a conductive polymer, is then formed on the dielectric. If necessary, the strip is cut into rectangles. The rectangles may be combined in parallel to form a capacitor package. Terminal leads and molding are added to form a surface mountable capacitor.
The drive to reduce the size of electronic products, and in particular to make very thin electronic products, demands that capacitors become correspondingly thinner. There is a need for an ultra-thin, surface mountable capacitor package that is on the order of the thickness of a silicon chip which is typically less than 0.508 mm (0.020 inches) thick and preferably less than 0.254 mm (0.010 inches) thick, and/or an ultra-thin embeddable capacitor that can be embedded within a printed circuit board layer without increasing the board layer's thickness which is again less than about 0.508 mm (0.020 inches) thick and preferably less than 0.254 mm (0.010 inches) thick. The present invention provides a method for thin solid electrolytic capacitor formation.